Material mixers having cylindrical rotatable drums providing a mixing chamber for particulate materials are used to mix animal feeds and roughages. The drum is driven with a power driven transmission to mix particulate materials through combined turning and tumbling action. An enclosed conveyor having a fixed auger trough, is used to carry the material from the drum chamber to a discharge opening. This machine does utilize the full capacity of the conveyor to facilitate thorough mixing of the particulate materials. A machine having a cylindrical drum with an open top mounted on a generally horizontal shaft to mix material is disclosed in U.S. Pat. No. 1,708,947. A plurality of mixing blades are mounted on the shaft whereby rotation of the shaft will mix material within the drum. The drum is rotated to facilitate the discharge of the material from the drum chamber through a discharge chute.